Cellular immunity is carried out by T cells that recognize antigens on the surface of antigen-presenting cells. The most potent antigen-presenting cells are the highly specialized dendritic cells. Other antigen-presenting cells include macrophages and B cells. Although macrophages and B cells can present antigens efficiently to memory T cells, they are less efficient than dendritic cells in initiating immune responses mediated by naive T cells.
Induction of T cell responses is known to be critical for anti-tumor effects. Recent development of techniques in generating dendritic cells in large numbers in vitro from peripheral blood monocytes or hematopoietic progenitors has led to new approaches in cancer immunotherapy.